Arterial Lines - developinganaesthesia



ARTERIAL LINES

Introduction

Arterial lines are the most accurate means of monitoring a patient’s blood pressure.

As such they should always be considered in any “unstable” patient in whom ongoing arterial monitoring is desirable.

In addition, patients who require repeated blood gas sampling should be considered for an arterial line to spare them the distress of repeated “needling”.

Indications

1. Continuous and real time blood pressure monitoring.

2. Frequent blood gas sampling.

Contraindications

Absolute

1. Infection over the proposed puncture site.

2. Absent collateral circulation:

● Evidence of which may be seen after insertion of the line with the subsequent development of an ischemic hand. If this occurs the line must be removed and an alternative site found.

● The historical Allen’s test for the adequacy of the hand circulation is no longer recommended.

The Allen’s test is not predictive of ischemic damage after cannulation and may not even correlate with abnormal flow. 2, 3

3. Occlusive small vessel disease, including:

● Buerger’s disease

● Severe Raynaud’s Disease.

4. A-V shunt for dialysis

5. Uncooperative patient.

Relative

● Bleeding diathesis

● Traumatic injury proximal to the proposed insertion site.

Complications

1. Arterial damage including:

● Laceration.

● Aneurysm formation.

● A-V fistula formation.

2. Hematoma.

3. Ischemia distally to the hand, (often transient in 10 %), or proximal forearm.

4. Distal emboli, (low).

5. Thrombosis, this can be related to:

● Duration of use (risk increases with increased duration)

● Size of cannula (18G > 20G), wrist size (related to arterial diameter).

● Catheter material, (Teflon is best)

● Flush system.

● Prolonged systemic hypotension.

● Number of cannulation attempts.

6. Infection.

7. Accidental disconnection, (may be fatal if subsequent bleeding goes unnoticed)

8. Inadvertent drug administration.

Technique of Arterial Cannulation

Sites of Arterial Cannulation

The preferred site for arterial cannulation is the radial artery.

If this is not possible the following are also suitable:

● Brachial artery

● Common femoral artery, (with the use of a single lumen “Arrow” CVC line)

● Dorsalis pedis artery.

Techniques used include:

● Direct entry

● Transfixion technique.

● Seldinger technique.

Transfixion Technique

1. Dorsiflex wrist

● Place folded towel or saline bag between wrist and armboard.

● The palm may be taped to maintain position.

2. Prep and drape wrist.

3. Infiltrate local anesthetic, if patient is conscious.

4. Insert pink “sureflow” catheter into artery at 45-degree angle.

5. When a “flash” of blood is seen, advance the catheter through the artery to transfix it

6. Remove the needle, leaving the plastic cannula in place.

7. Attach 3 ml syringe half filled with saline to the cannula and withdraw slowly at the same time gently aspirating.

8. As soon as blood fills the cannula stop withdrawing and then advance the cannula into the artery.

9. Remove syringe and attach reflux valve.

10. Attach arterial line to the reflux valve.

11. Flush the arterial line to ensure it is running properly.

12. “Zero” (calibrate) the line:

● Close the 3-way valve to the patient, so the line is open to the atmosphere.

● “Zero” the line.

● Close the line to the atmosphere and flush line.

Arterial Wave Form Interpretation

Information available from the arterial waveform includes:

● Steep rise and fall (hyperdynamic pulse), sepsis, anemia, thyrotoxicosis, pregnancy, aortic regurgitation and AV fistula.

● Increased systolic variation during the respiratory cycle: hypovolemia, high intrathoracic pressure, sever LV dysfunction and tamponade.

● Myocardial O2 supply vs O2 demand, indicated by the area under systolic portion of the curve vs area under diastolic portion.

● Hypovolemia causes an increased respiratory swing in systolic, lower dichrotic notch, steeply peaked systolic wave.

● LV systolic dysfunction causes flattening of up-slope, reduced peak pressure.

Misinformation from arterial pressure monitoring may include:

● Poor guide to perfusion.

● Poor guide to myocardial performance.

● Over estimates aortic systolic pressure due to reflected pressure waves (pedal > radial > femoral > aortic)

● Technical limitations: amplification, resonance etc resulting in wave distortion.

● Overestimation of pressure with tachycardia or gas bubbles in the transducer line.

Factors Influencing Signal Fidelity

Equipment factors, which optimize signal fidelity

● High frequency response transducer.

● Short stiff non-compliant tubing.

● Bubble free eg small air bubbles < 0.25 mls produce under damping, whilst larger air bubbles produce over damping.

● Slow continuous flush device (1-3 ml/hr results in < 2 % error)

● Transducer zero and calibration against a mercury column.

Patient factors which reduce signal fidelity

● Rapid heart rate, (resonance)

● High frequency reflections, eg elderly, high SVR, arteriosclerosis.

● Site of catheter, (radial versus femoral versus axillary versus aorta)

Management of Arterial Lines

1. The cannula must be visible at all times, (to enable detection of disconnection and hemorrhage)

2. Maintain the pressure bag at 300 mg Hg, (marked out by the green line)

3. Use sterile technique when withdrawing blood, flushing line or changing bags.

4. Always flush the line after taking blood samples or “zeroing” the monitor.

5. Discard the initial 5 mls of blood prior to blood sampling.

6. Always ensure that there is no air in the line.

7. Note that arterial lines can only be managed for inpatients in HDU/ICU. They cannot be managed on the general wards

References

1. Arterial Cannulation Insertion, in Atlas of Bedside Procedures, Vander Salm, TJ, 2nd ed 1988.

2. Slogoff et al. On the safety of radial artery cannulation. Anesthesiology 1983 59:42-47. 

3. Wilkins et al Radial artery cannulation and ischaemic damage: a review. Anaesthesia 1985 40:869-899. 

Dr J. Hayes

Reviewed 26 March 2009

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